MUSCULAR SYSTEM. 95 



Relations. — Externally, with the panniculus carnosus, cellular 

 tissue, and branches of the portio dura; internally, with parts of 

 the superior and inferior maxillae, buccinator, mass of yellow fat 

 filling the intermaxillary vacuity, posterior and anterior masseter 

 arteries and veins; superiorly, with the temporal artery and vein; 

 posteriorly, with the parotid gland ; anteriorly, with the parotid 

 duct, anterior maxillary artery and vein. 



Diiectiun. — Oblique: from above, downwards; and from be- 

 fore, backwards. 



Structure. — Of its exterior, the superior two-thirds is aponeuro- 

 tic ; internally, it is composed of several distinct fleshy layers, 

 separated by aponeurotic intersections. 



Action. — In co-operation with the former muscle, to elevate 

 the lower jaw, and maintain it in approximation against the upper. 



STYLO-MAXILLARIS. 



Situation. — Behind the lower jaw. 



Figure. — Pyramidal : base turned downwards and forwards. 



Attaclnnent. — Superiorly and posteriorly, to the styloid process 

 of the occipital bone : inferiorly and anteriorly, to the angle of the 

 lower jaw. 



Relation. — Externally, with the parotid gland, temporal and 

 occipital branches of the jugular vein, and the arteries piercing the 

 gland ; internally, with the membrane bounding the guttural ca- 

 vities; superiorly, with the stylo-hyoideus. 



Direction. — Oblique: from behind, forwards; and from above, 

 downwards. 



Structure. — Tendinous, at its occipital attachment; remainder 

 fleshy, intersected with layers of tendon, and having aponeurotic 

 stripes along its surfaces. The posterior division of the digastri- 

 cus is inseparably united with the inferior border. 



Action. — To draw the jaw backward, and at the same time 

 depress it: it therefore assists in opening the mouth, and so far 

 is an antagonist to the two former muscles. 



PTEKYGOiDEUS INTERN US. — SpImio-maxUlaris. 



Situation. — The same relative position upon the inner side of 

 the jaw to what the masseter has upon the outer, filling up the 

 excavation there in the bone. 



Form. — Broad and flat; terminating, inferiorly, in a semicircu- 

 lar border, from which it narrows, upwards. 



Attachment. — Superiorly, to the pterygoid process, and crus of 

 the sphenoid bone, to the palate bone, and to the tuberosity of the 

 superior maxillary bone : inferiorly, to the fossa which it occu- 

 pies, and around the angle of the jaw. 



